[throwaway0a5e]

Except in cases where the transportation is highly specialized and optimized (e.g. a pipeline) you are going to have a hell of a time finding an example of human activity where the minimum environmental impact is not on the order of mass * distance.

[bayindirh]

OTOH, environmental impact, regardless of its distance to humans, never stays isolated to the place where it's happening.

It always affects distant places, human population or not.